The present invention relates to an improved electrical control system, such as may be used to operate a central vacuum cleaning system. The control system will operate a centrally located vacuum turbine motor (or other electrical device) and a remote vacuum cleaning agitator motor (or other electrical device).
In many typical conventional systems, the operating voltage (e.g. 110-125 volts) for the electrical device is provided directly at the wall plate or other receptacle and is present at the receptacle independent of whether the device is connected to the receptacle or not. This presents an unnecessary electrical safety hazard during periods of non-use, or when the device is connected but switched off.
U.S. Pat. No. 3,525,876, is directed to a two-wire power transmission and control circuit which supplies low voltage D.C. power to an agitator motor and which uses a low voltage A.C. control circuit. While the circuit and method described in that patent works satisfactorily in some situations, certain problems, both physical and electrical, may arise because major circuit components had to be constructed in the handle of the remote cleaning unit hose.
U.S. Pat. No. 4,070,586 solved some of the problems associated with then conventional systems, including the system described in U.S. Pat. No. 3,525,876 by providing a system in which the handle of the cleaning unit hose contained only a simple single-pole double-throw switch with a center OFF position together with a small resistance that was used to draw a small current through the wire pair when it is desired to use the A.C. vacuum system without energizing a nominal low-voltage (24 VAC) agitator motor. The wire pair, which is connected through a suitable receptacle associated with the vacuum hose receptacle, was coupled to a power source and the control circuitry which is preferably located at the opposite end of the vacuum cleaning airway at the centrally located A.C. powered vacuum turbine system. The control circuitry included a current sensor which, upon sensing a current in the circuit to either the 24 VAC agitator motor or through the resistance located in the handle of the remote cleaning unit, activated circuitry that energizes the nominal 120 VAC motor coupled to the vacuum turbine. Thus, the operator was able energize the vacuum system by creating a current flow through the low voltage wire pair either by switching on the agitator motor with the turbine motor, or by switching to the resistance that shunted the agitator motor but still provided power to the vacuum turbine motor. U.S. Pat. No. 4,070,586 was thus directed at structure and method for controlling the 120 VAC vacuum turbine motor from a handle mounted switch using a particular two-wire circuit. Unfortunately, this circuit provided 120 VAC to both the vacuum turbine motor and the agitator motor through a single pair of conductors conducting 120 VAC, in order to achieve the desired results. Therefore, while the system and method of U.S. Pat. No. 4,070,586 and the Reexamination certificate B1 4,070,586 provided a very good operational and safety characteristic, additional improvements, not realized at the time, could still be made.
For example, there remained a need for a equipment generally, and for portable and stationary vacuum cleaning equipment in particular, that utilizes a safe Class-2 voltage for control unless the equipment is actually being operated and requires higher voltage, such as a 110-125 volt alternating current (VAC) operating voltage, so that neither the operator nor any service technician are exposed to potentially dangerous voltages when connecting or disconnecting the equipment or when operating the equipment.